Since its successful development in 1990s, the lithium ion secondary battery has gradually been replacing traditional alkaline secondary batteries such as the nickel cadmium battery and the nickel hydrogen battery as it has a large specific energy, high working voltage, low self-discharging rate, long cycling life, and is non-polluting. It is widely used in modern mobile electronic and communications equipment, such as cell phones, notebook computers, portable computers, personal digital assistants (PDA), video cameras, digital cameras, portable DVD/VCD and MP3 players.
Currently, the commercial lithium ion battery pack is comprised of a metal shell and cover holding the electrode core and electrolyte, as well as other accessories such as the protection circuit and a plastic outer shell. There are several disadvantages to this type of battery pack.
First, the assembling of the metal shell and its contents is complicated. The formation of the metal shell requires multiple deep cuts as well as edge cutting, rinsing and heat drying. Stamped and partial injection is needed to form the cover. In addition, the assembling of the electrode pole and cover also requires multiple processes. The complexity of fabricating the metal shell and cover, together with the increased complexity of the assembly cause complications, lengthy production cycles, and high manufacturing costs.
Short-circuiting between the electrode core and the conducting metal shell and cover can easily occur, resulting in safety problems. To overcome this, several types of protection methods have to be adopted, again increasing the complexity of the battery and the cost of manufacturing.
Third, the metal shell and cover plate, together with their contents, and the supplementary protection installments all have to be placed inside a battery package. This significantly increases the weight and volume and decreases the gravimetric energy density and volumetric energy density of the battery. With the present day demand for high capacity, lightweight, and low cost batteries, an urgent solution to this problem is needed.
Fourth, there are numerous inter-welded spots inside this battery configuration. These welded spots occur at contact points such as those between the negative electrode tab and the connection plates; the connection plates and the cover board, and, the positive electrode and the cover. They can increase the internal resistance, heating, and the probability of the emergence of potential problems.
Due to the limitations of the prior art, it is therefore desirable to have novel lithium ion secondary batteries that are lightweight, have high energy densities, simple to manufacture, and low in costs.